Why was the Roosevelt Corollary a very important step in US foreign policy especially toward Latin America?

Well, the Roosevelt Corollary stated that the United States would pay off the debts of Latin American countries in order to keep Europe out. Roosevelt feared that European powers would loan money to these countries and thus become involved in the western hemisphere (a violation of the Monroe Doctrine). Because of this, this was an extension of the Monroe Doctrine, and became a part of the US foreign policy.
The Roosevelt corollary is important because it added to the Monroe Doctrine in matters of foreign military actions.